Water accounting in the

Nile BasinNile Basin Focal Project

February 2009

Y. Mohamed; D. Molden; W. Bastiaanssen

Nile water accounting: Objectives

• Assess water resources, uses, and productivity– Quantify simple indicators: water balance, water use,

and water productivity.

– Use RS data as key inputs: P, ET, Biomass

– Assess potentials and limitations of the methodology

• Nile water management: opportunities and constraints

Nile water accounting: Methodology

• Based on water balance principle

• Define indictors: supply, consumption, beneficial, non-beneficial

• Boundary conditions (Inputs): – Water Supply: Rain, River, Groundwater

– Water use: Consumptive (ET), non-consumptive, beneficial (T), non-beneficial (E), committed (treaties), etc.

• Scales:– Spatial: catchment, production system, sub-basin,

basin, country

– Temporal: month, season, annual, long term mean

• Output– Water accounting water productivity

Source: Molden, 1997

>1600

1400 - 1600

1200 -1400

1000 - 1200

200-400

400 - 600

600 - 800

800 - 1000

< 25

25 - 50

50 - 100

100 - 200

Mean PMean ET0

Nile Hydrology:

Nile Water use

Input: Land and water use classes

MWsaline sinks15

MWmanaged wetland14

NLnatural lakes and rivers13

MWreservoir12

MWirrigated crop11

NLdesert10

MWUrban + industustry9

MLrainfed crops8

NLnatural wetland7

NLsparse savanna6

NLopen savanna5

NLwoody savanna4

NLshrub land3

NLopen forest2

NLclosed forest1

classLand useNo.

Input: Rainfall in 2007

FEWS TRMM

Input: SEBAL ET, T, E

Input: SEBAL Biomass

Land use and water use (=consumption)

0

200,000

400,000

600,000

800,000

1,000,000

close

d fore

stop

en fo

rest

shrub

land

woody

sava

nna

open

sava

nna

spars

e sav

anna

natur

al wetl

and

rainfe

d crop

s

Urban+

indus

t.de

sert

irriga

ted cr

opres

ervoir

lakes

& riv

ers

manag

. wetl

and

salin

e sink

s

Are

a K

m2

0

400

800

1200

1600

2000

ET k

m3/

yr,

P m

m/y

r

Area km2ET km3Rainfall

Natural land cover Managed land use Managed water useNatural forest P, ETSavanna P, ETDesert P, ET.. P, ET

Forest plantation P, ETRainfed crop P, ET.. P, ET

Irrigation P, ETManaged wetlands P, ETDrinking water P, ET.. P, ET

outflow

inflow

Aquifer & reservoirs

Water balance for 2007 in km3

62.4 -53.7

15.8

6.0

0.01.0

Committed 6.0

Water balance components

– Total water supply =

– Available Water =

– Diverted Water =

– Consumed water =

– Outflow water =

– Excess water =

CommittedETPETPInflow MLNL −−+−+ )()(

PInflow+

MWETP )( −

∑ MWMlNLET ,,

SdivertedETPInflowMLNL

∆+−−+∑ ,)(

CommittedOutflow−

Water balance components

water balance components

1730

64.4 53.7

1714

11 60

500

1000

1500

2000

water supply Available diverted consumed Excess Committed

km3

Water balance indicators

– Consumed fraction =

– Available fraction =

– Diverted fraction =

– Excess fraction =

– Committed fraction =

)(,,

PInflowET MWMLNL

+∑

)( PInflowAvailable

+

AvailableDiverted

AvailableExcess

OutflowCommitted

Water balance indicators

Water Balance indicators

0.00

0.25

0.50

0.75

1.00

Consumed Available Diverted Excess Committed

Water consumption

water consumption

1446

198 70

1309

719 590 388

0500

100015002000

natur

al lan

d cov

erman

aged

land

use

manag

ed w

ater...

Benefi

cial

Benefi

cial-E

c...

Benefi

cial -E

nvi...

Non-be

nefic

ial

ET,

km3

Water consumption indicators

– ET Natural land cover =

– ET Managed land use =

– ET Managed water use =

– ET Beneficial water use =

– ET Beneficial – Economics =

– ET Beneficial – Environment =

∑ MWMLNL

NL

ETET

,,

∑ MWMLNL

ML

ETET

,,

∑ MWMLNL

MW

ETET

,,

∑ MWMLNL

ben

ETET

,,

∑ ben

Econben

ETET

∑ ben

Envben

ETET

Water use indicators

Water consumption indicators

0.00

0.10

0.20

0.30

0.400.50

0.60

0.70

0.80

0.90

Natural LU Managed LU Managed WU Beneficial ET Ben_Env. ET Ben_Env. ET

Food FishWoodFeed Industrial

Economic productivity sheet

Rainfed cropsIrrigated crops

PasturesSavanna

ForestBushland

FishpondLakes

IndustriesPorts

Hydropower

Reservoir

1.6Kg/m3

1.3Kg/m3

4.5Kg/m3

Kg/m3 $/m3 1.0 Kw/m3

Discussions

• Water accounting at basin scale is effective to understand supplies, uses and production of major systems

• Major part of Nile water is consumed, mainly by natural land cover, and managed land use, not necessarily non-beneficial.

• Still there is excess )not closed)

• Future work:– Refine water consumption by different systems (livestock, fisheries, environment,

etc.)

– Refine estimates of productivity (not only biomass)

– More validation on P, ET, T, E

– Spatial calculation, sub-basins, countries,

– Compute accessibility